Use the FeatureDefinitions property of the SPFarm class to get the collection of Feature definitions that are installed in the server farm. To add a Feature definition to the collection, use one of the SPFeatureDefinitionCollection methods of the SPFeatureDefinitionCollection class. Adding a Feature to the collection installs the Feature in the server farm, making it available for activation in its specified scope. Adding a Feature that has farm scope not only installs the Feature, but activates it within the farm.

Use an indexer to return a single Feature definition from the collection. For example, if the collection is assigned to a variable named myDefinitions, use myDefinitions[index] in C#, or myDefinitions(index) in Visual Basic, where index is the Guid of the Feature.

Caution:
You cannot use the SPFeatureDefinition constructor to create a Feature definition object. This is not supported and returns a NullReferenceException if you attempt to implement members of an object created through the constructor.

The following example installs a Feature definition in the server farm. The example assumes that a custom folder has been added to the Features directory that contains a feature.xml file specifying a Guid for the Feature. This example requires using directives (Imports in Visual Basic) for both the Microsoft.SharePoint and Microsoft.SharePoint.Administration namespaces.

[C#]

System.Globalization.CultureInfo cInfo = new System.Globalization.CultureInfo(1033);

SPFeatureDefinitionCollection farmFeatures = SPFarm.Local.FeatureDefinitions;

Guid farmGuid = new Guid("BCFC1029-7DB4-4e9c-B162-B03CE8497DAC");

SPFeatureDefinition featureDefinition = farmFeatures.Add(@"Feature_Folder\Feature.xml", farmGuid, true);

Response.Write("Farm definition " + SPEncode.HtmlEncode(featureDefinition.GetTitle(cInfo)) + " added.<BR>");